Evidence of sub-10 nm particles emitted from a small-size diesel engine

Particle size distributions (PSDs) are measured at the exhaust of a diesel engine burning a sulphur-free diesel fuel and a blend of the fuel with a rapeseed methyl-ester. Different operating conditions of load and engine speed are analyzed. Particles with sizes ranging from few nanometers up 1 mu m are generated during combustion in the engine. Operating conditions and fuel characteristics strongly affect the PSDs confirming that particles are generated from fuel oxidation and pyrolysis rather than from the oxidation of lube oil or from other sources in the engine. The higher is the engine load, the higher the emission of mass concentration of particulate matter but the lower their number concentration. At fixed engine loads, the increase of the engine speed produces more particles and with larger mean sizes. The use of the biofuel blended with a commercial fuel reduces the total mass concentration of particulate matter but strongly increases the number concentration of sub-10 nm particles.